Cyclic Fatigue Resistance of OneShape in Two Different Radii of Curvature

Objectives: The purpose of this study was to compare the fracture resistance to cyclic fatigue of OneShape (Micro-Mega, Besancon, France) single-use rotary nickel-titanium instruments in artificial canals with two different radii of curvature.
Methods: A total of fifty new OneShape instruments were selected and randomly divided into two groups (n=25 each) based on radius of curvature. Cyclic fatigue testing was performed using a device which allowed the instruments to rotate freely in a stainless steel artificial canals with radii of curvature of 5 and 10mm. Each instrument was rotated until fracture occurred and the number of cycles to fracture (NCF) was calculated by multiplying time to fracture and rotational speed. Data were subjected to independent samples t-test (α=0.05).
Results: The averages of NCF of samples were 501.5±32.5 (5mm radius) and 986.6±177.3 (10mm radius), respectively. The mean NCF for 5mm radius group was significantly less than 10mm radius group (p<0.001).
Conclusions: According to the results of this study, radius of curvature had a crucial role on fracture resistance of OneShape instruments. Thus, clinically it should be used cautiously in abruptly curved canals.